The disclosure of Japanese Patent Application No. 2000-108156 filed on Apr. 10, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a fuel pressure control apparatus and method of an internal combustion engine.
2. Description of Related Art
Generally, in a type of internal combustion engine that supplies fuel into a combustion chamber by directly injecting fuel into the chamber, a high-pressure fuel pump is provided for ejecting fuel toward a fuel delivery pipe. By adjusting the amount of fuel ejected from the high-pressure fuel pump through the control of the drive timing of the pump, the fuel pressure in the fuel delivery pipe (the pressure of fuel supplied to a fuel injection valve) is controlled. In this control of fuel pressure, the fuel pressure rises if the amount of fuel ejected from the high-pressure fuel pump is increased. If the amount of fuel ejected from the high-pressure fuel pump is reduced, the fuel pressure decreases.
A control amount used for controlling the drive timing of the high-pressure fuel pump is calculated such that an amount of fuel ejection requested of the pump can be achieved, based on the drive timing that provides a maximum amount of fuel ejection of the pump (maximum ejection timing). More specifically, the control amount is calculated based on a feed-forward term that is a value corresponding to the amount of fuel injected from the fuel injection valve, a proportional term that increases or decreases a deviation between the aforementioned fuel pressure and a target value of the fuel pressure so that the deviation becomes xe2x80x9c0xe2x80x9d, and an integral term that is updated to an increased side or a reduced side in accordance with the aforementioned deviation.
By controlling the drive timing of the high-pressure fuel pump through the use of the control amount calculated as described above, a requested amount of fuel ejection can be obtained.
The amount of fuel ejected from the high-pressure fuel pump increases as the control amount increases and therefore the drive timing of the pump is advanced. Conversely, if the control amount decreases and therefore the drive timing of the pump is retarded, the amount of fuel ejected decreases. The upper limit value of the control amount is a value corresponding to the maximum ejection timing since the control amount is calculated based on the maximum ejection timing providing the maximum amount of fuel ejection. Thus, when the-control amount reaches the value corresponding to the maximum ejection timing providing the maximum amount of fuel ejection, the amount of fuel ejected from the high-pressure fuel pump reaches a maximum value.
However, high-pressure fuel pumps vary in fuel ejection characteristic due to their individual differences. Therefore, even if the control amount remains the same, the amount of fuel ejection varies among individual pumps. It is conceivable to perform a learning operation so as to prevent the amount of fuel ejected from a high-pressure fuel pump from assuming a value excessively deviated from a proper value due to the aforementioned variations. Such a learning operation is used in a fuel pressure control apparatus described in, for example, Japanese Patent Application Laid-Open No. 8-232703.
In such a learning operation, the control amount is corrected by using a learned value that is a value corresponding to the deviation of the amount of fuel ejection from the proper value. The learned value is a value that is increased or decreased so as to converge the value of the integral term used for calculating the control amount into a predetermined range. That is, since the learned value is increased or decreased so as to converge the integral term into the predetermined range while the integral term is updated so as to prevent excessive increases of the deviation of the amount of fuel ejection from the proper value, the learned value is obtained as a value corresponding to the deviation of the amount of fuel ejection from the proper value. Therefore, by correcting the control amount through the use of the learned value, excessive deviations of the amount of fuel ejection from the proper value caused by the aforementioned variations are substantially suppressed.
The correction of the control amount by the learned value can suppress excessive deviations of the amount of fuel ejection of the high-pressure fuel pump from the proper value. In high-pressure fuel pumps, however, due to the individual variations in fuel ejection characteristic, the maximum ejection timing providing the maximum amount of fuel ejection also varies among individual pumps. Even if the maximum ejection timing providing the maximum amount of fuel ejection varies, the execution of the learning operation described in the aforementioned laid-open application does not change the drive timing providing the maximum amount of fuel ejection used for the calculation of the control amount. Therefore, if the control amount is set to a value (upper limit value) corresponding to the drive timing providing the maximum amount of fuel ejection, the maximum amount of fuel ejection is not achieved, so that it takes an added amount of time to raise the fuel pressure to a target value by setting the control amount to the upper limit value at the time of a start of the engine or the like.
Accordingly, it is an object of the invention to provide a fuel pressure control apparatus and method of an internal combustion engine that is capable of reliably achieving a theoretical or designed maximum amount of fuel ejection of a fuel pump.
A first aspect of the invention relates to a fuel pressure control apparatus of an internal combustion engine including a fuel pump for ejecting fuel toward a fuel delivery pipe, and a controller that adjusts an amount of fuel ejection of the fuel pump by controlling a drive timing of the fuel pump. The fuel pressure control apparatus controls the fuel pressure in the fuel delivery pipe. The controller calculates a control amount to be used for controlling the drive timing of the fuel pump, based on a maximum ejection timing that provides a maximum amount of fuel ejection of the fuel pump, and learns a drive timing of the fuel pump that provides the maximum amount of fuel ejection, as the maximum ejection timing.
According to the above-described aspect of the invention, it becomes possible to calculate a control amount that provides the maximum amount of fuel ejection by calculating the control amount based on a,learned maximum ejection timing. Then, by controlling the drive timing of the fuel pump based on the control amount, the designed maximum amount of fuel ejection of the fuel pump can be achieved.
In the above-described aspect of the invention, the controller may calculate the control amount so that an amount of fuel ejection requested of the fuel pump is achieved, and may learn the maximum ejection timing based on values of the control amount provided under a plurality of engine operation states that differ in the amount of fuel ejection requested of the fuel pump.
According to this aspect of the invention, the actual fuel ejection characteristic of the fuel pump is estimated from the values of the control amount provided under the engine operation states that differ in the requested amount of fuel ejection. Then, the maximum ejection timing can be precisely learned from the estimated actual fuel ejection characteristic.
In the above-described aspect of the invention, the controller may calculate the control amount so that the amount of fuel ejection requested of the fuel pump is achieved, based on a deviation between a fuel pressure in the fuel delivery pipe and a target value of the fuel pressure.
According to this aspect of the invention, the control amount that provides the requested amount of fuel ejection can be precisely calculated. Therefore, the values of the control amount under the engine operation states that differ in the requested amount of fuel ejection become precise values. Hence, the actual fuel ejection characteristic of the fuel pump can be precisely estimated from the values of the control amount.
In the above-described aspect of the invention, the controller may learn the maximum ejection timing based on values of the control amount provided under a plurality of engine operation states that differ; in the amount of fuel ejection requested of the fuel pump at a fixed engine revolution speed.
The actual fuel ejection characteristic of the fuel pump changes depending on the engine revolution speed. According to the above-described aspect of the invention, the actual fuel ejection characteristic of the fuel pump can be precisely estimated from the values of the control amount provided under the engine operation states that differ in the requested amount of fuel ejection at the fixed engine revolution speed. If a maximum ejection timing is learned based on the thus-estimated actual fuel ejection characteristic, the learning can be more precisely performed.
In the above-described aspect of the invention, the controller may learn the maximum ejection timing for each of a plurality of learning regions that are divided in accordance with an engine revolution speed.
As the fuel ejection characteristic changes with changes in the engine revolution speed, the drive timing that provides the, maximum amount of fuel ejection also changes. According to the above-described aspect, however, the maximum ejection timing is learned with respect to each of the learning regions divided in accordance with the engine revolution speed. Therefore, by learning control amounts based on the maximum ejection timings of the learning regions corresponding to engine revolution speeds, it becomes possible to precisely achieve the designed maximum amount of fuel ejection of the fuel pump regardless of the engine revolution speed.